The present invention relates to an apparatus for setting and retaining a fixed direction in an essentially horizontal plane. The main field of application of such an apparatus is the alignment, and particularly the repeated alignment, of a tool such as a drill or the like. Alignment problems of this kind arise when drilling rock, in workshop practice, etc.
When working, e.g., with a rock drill, it may be necessary to drill a series of holes which are to be as parallel with one another as possible. The holes can extend either in an essentially horizontal or in an essentially vertical plane at a specified inclination to one of these two planes, depending on whether the drilling is made, e.g., in a wall, in a bottom or in a ceiling. In the last mentioned case, but also in tunnel driving or the like, it is particularly important that the bore holes be parallel one with another according to two coordinates, i.e., so that they all not only extend in the same plane, but also at invariable mutual distance. When drilling in a horizontal plane, this requirement means in effect that each drilling must be effectuated both in a single plane and parallel one with another.
These requirements are difficult to meet in practice, mainly because at the transfer of the rock drill from the place where one hole or one series of holes has been made to the place of another hole or hole series, the slope of the ground often changes. It is therefore not possible simply to retain the relative position between the drill feeder and the machine stand, as adjusted at the first drilling.
An automatic levelling control and clinometer has been proposed in the U.S. Pat. No. 2,893,134 for holding the scraper blade of a road grader at a predetermined angle of inclination (i.e., direction in a vertical plane) which clinometer in one embodiment has a tilt-responsive position sensor in the form of a V-shaped tube of non-conductive material, partially filled with an electrically conductive fluid such as mercury. Through the tube extends lengthwise a resistance wire which is thus partially immersed in the volume of mercury. The mercury volume is at its lowest point connected to a meter, via an intermediate contact in the tube, while the resistance wire is connected at both ends to a pair of resistors in a bridge circuit of the Wheatstone type. The other pair of resistors in this bridge circuit is formed by those legs of the resistance wire, which are not shunted by immersion in the mercury in the tube.
An object of the present invention is to provide a setting device of the above type which can be used for position measurement or adjustment in or near a horizontal plane, with compensation for any vertical inclination that may occur.